JPS60121474A - Image forming device - Google Patents

Abstract

PURPOSE:To form a copied image of a stable density by counting the continuous generation time of a toner supply signal and switching a supply quantity per unit time from a hopper to a developing device to the second supply quantity if this signal is generated continuously for a prescribed time. CONSTITUTION:Before copying of an original, a standard black plate 19 is illuminated by a lamp 2, and an electrostatic latent image corresponding to the black plate 19 is developed by a developing device 20. The quantity of reflected light of the formed toner image is measured by a reflected light measuring circuit 22; and if this measured quantity is higher than a preliminarily set quantity of light, the circuit 22 sends a signal of a mode I to a DC servomotor driving circuit 23. The continuous generation time of the signal of the mode I is measured by a counter 24; and if this measured time exceeds a preliminarily set time, the signal is switched to a signal of a mode II, and this signal of the mode II is sent. The voltage applied to a DC servomotor 25 is controlled by the circuit 23 to control the supply quantity of toner due to a supply toner 12. Thus, a copied image of a stable density is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus such as a copying machine, and particularly to an image forming apparatus having a developing device using a two-component developer.

Generally, in copying machines that use two-component developers,
The developing device consists of a part of the hopper (replenishment toner tank) and a part of the developer (developing section), and has an automatic density adjustment mechanism (so-called A 'f') to compensate for toner consumption during the copying process. R) is provided. This A
The purpose of TR is to maintain a constant mixing ratio of toner and carrier in the developer section, and the method is to measure the reflectance or weight of the developer (toner and carrier) on a part of the developer or on the developing sleeve using a sensor. When the detected value is below or above a predetermined level, toner is replenished from part of the hopper to part of the developer to compensate for toner consumption due to copying. Alternatively, a chart with a certain predetermined density (usually placed at approximately the same height as the document surface) is illuminated with a document illumination lamp, and an electrostatic latent image corresponding to the chart is imaged by illuminating the photoreceptor with image exposure. , the latent image is visualized by a developing device, and the density of the obtained toner area image is measured by a detection means (a light emitting diode, a 7-tooth sensor, etc.),
A method has also been used in which when the value is below a predetermined level (the density is low), toner is replenished from a part of the hopper to a part of the developer.

The above two methods aim to keep the density of the copied image constant (mainly the maximum density Dmax), but the original used has many black areas (specifically, the II!II image ratio is about 15% or more). ), if continuous copying is performed, the replenishment of toner from part of the hopper to part of the developer cannot keep up with the toner consumption due to copying, so the density will gradually become lighter (and the image quality will deteriorate). Ta.

This is because if the toner replenishment from part of the hopper to the developer part is increased to correspond to copying, the i# image density will fluctuate due to toner replenishment when copying a normal original (image ratio of several percent). This is due to the fact that a small amount of toner needs to be supplied from a portion of Potsupa to a portion of Developer.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional examples, and to provide an image forming apparatus that can obtain a copied image with a stable density regardless of the image ratio of the copied original.

The present invention includes means for generating a toner replenishment signal, and means for counting the continuous generation time of the toner replenishment signal from the hopper to the developing device according to the toner replenishment signal, and the toner replenishment signal continues for a predetermined period of time. If this occurs, the image forming apparatus switches the replenishment amount per unit time from the hopper to the developing device from the first replenishment amount to the second replenishment amount.

The present invention will be described in detail below based on the drawings.

FIG. 1 is a schematic diagram of a copying apparatus to which the present invention is applied. In the figure, 1 is a platen glass, 2 is an original illumination lamp, and 6 is a reflective shade. lens 7,
The photosensitive drum 9 is
projected on top. This embodiment is a copying apparatus of a fixed type with an original table, and a lamp 29, a reflecting shade 39, and a reflecting mirror 4 are arranged on one unit, and the reflecting mirrors 5 and 6 move back and forth according to the copying process. It is on a separate unit and reciprocates at half the speed of the previous unit. 10 is a charger. Photosensitive drum 9
By performing image exposure on the charger 10 in advance,
As a result, a portion of the uniformly charged charges formed on the surface of the photosensitive drum 9 is erased, and an electrostatic latent image corresponding to the original is formed.

11 is a hopper, and 12 is a replenishment roller for replenishing toner from the hopper to the developer 16. The replenishment row 212 is controlled to rotate multiple times by a DC servo motor (not shown). Any type of replenishment roller may be used as long as it rotates to send the toner from the hopper to the developer, but in this embodiment, a sponge roller is used. The toner enters the cavity of the sponge,
It will automatically drop to developer 16. The replenished toner is mixed with carrier in the developer 13.

Usually stirring is carried out using a 5M stirring blade, but this is not particularly shown. 14 is a developing sleeve. 15 and 16 are a transfer corona discharger and a separation corona discharger, respectively. Also 17
The light emitting diode 18 is a photosensor. 19 is a standard blackboard having a predetermined density.

Now, the electrostatic latent image corresponding to the document formed on the photosensitive drum 9 is visualized by the toner on the sleeve 14 of the developing device 2o, and is transferred to the transfer paper P through a transfer process and a separation process. .

In this copying apparatus, the automatic density control mechanism is as follows. First, before copying the manuscript,
-Q - A portion other than the document portion in the leading edge direction of the document, that is, a standard blackboard 19, is illuminated with the lamp 2, an electrostatic latent image corresponding to the blackboard 19 is formed, and the latent image is visualized by the developing device 20. do. The formed toner image is illuminated by 17 LEDs, and the reflected light from the toner image is measured by the photo sensor 18. When the measured value is above a predetermined level (the amount of reflected light is greater than the predetermined value), replenishment is performed. Rotate the row 212. The above-mentioned illumination of the standard blackboard 19 and measurement of the toner image reflected light are carried out in step 1.
It is common and most effective to perform this for each copy. Further, the timing of measuring the reflected light can be determined using encoder pulses or the like.

Next, embodiments of the present invention will be described in more detail.

FIG. 2 is a block diagram of the automatic density control mechanism of this embodiment, and FIG. 3 is a flowchart showing the relationship between the amount of reflected light and the generated signal. Clock pulse generation circuit 21
Accordingly, at the measurement timing, the reflected light measuring circuit 22 measures the amount of reflected light of the toner image corresponding to the standard blackboard 19 using the light emitting diode 17 and the 7th sensor 1B (step 1).

If the amount of light is larger than the preset amount of light, a mode 1 signal is generated to the DC servo motor drive circuit 26 (
Step 2). Further, if the measured amount of reflected light is smaller than the preset amount of light, no signal is generated. The amount of reflected light is further measured at the timing of the clock pulse (step 3). If the amount of reflected light is greater than the preset amount of light, the time during which the mode 1 signal is continuously generated is further counted by the counter 24 (step 4). When the continuous generation time exceeds a preset time, a mode (2) signal is generated to the DC servo motor drive circuit 23 (step 5). At this time, if the mode I signal is not generated even once, the counter 24 is reset.

The DC servo drive circuit 26 controls the voltage applied to the I)C servo motor 25 based on the signals of mode I and mode (2) described above. That is, the voltage applied to the DCC servo motor in mode I is controlled so that ■■<■■, where the voltage applied to the DCC servo motor in mode I is V■ in mode 11.

1) If the voltage applied to the C servo motor is changed, the rotation speed of the motor changes, and the rotation speed of the toner replenishing roller 12 changes.
In other words, according to the present invention, when the image ratio of the original is small, toner replenishment is performed in mode I.
(first replenishment amount), when the image ratio of one document is large (in other words, toner consumption is high), toner replenishment is in mode 1.
By setting +mode (2) (second supplementary line amount), copies with stable image density can always be obtained regardless of the image ratio of the original.

In the embodiment of the present invention, an example was shown in which a standard blackboard was used to measure the amount of reflected light from a toner image on a drum. However, instead of using a standard blackboard, it is possible to measure a toner image on a photoreceptor using 0N-OFF during blank exposure. Alternatively, the amount of light reflected from this toner image may be measured.

Further, the present invention is also applicable to a system in which the density is controlled by measuring the ratio of toner and carrier on the developing sleeve.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the copying apparatus, FIG. 2 is a block diagram of the automatic density control mechanism, and FIG. 3 is a flow chart. In the figure, 12---Replenishment roller, 1711...Light emitting diode, 18II...Photo sensor, 19...
Standard blackboard 20 represents a developing device. Applicant Canon Co., Ltd.

Claims (1)

[Claims] An image forming apparatus comprising means for generating a toner replenishment signal and means for quantitatively replenishing toner from a hopper to a developing device based on the toner replenishment signal, the image forming apparatus comprising means for counting a continuous generation time of the toner replenishment signal. ,
When the toner replenishment signal occurs continuously for a predetermined period of time,
The amount of replenishment per unit time from the hopper to the developing device is
An image forming apparatus characterized by switching to a replenishment amount of .